Simulation of Mesoscale Convective Systems and Extreme Rainfall Events over West Africa Using MPAS-A.

Mesoscale Convective Systems (MCSs) are the dominant source of extreme rainfall and flooding in West Africa, driving most high-impact precipitation events in the region. This study investigates an extreme rainfall event that occurred between May 26 and May 30, 2025, over Mokwa, Niger State, Nigeria, using the Model for Prediction Across Scales-Atmosphere (MPAS-A), a global cloud-resolving model. The MPAS-A simulation is used to examine the development and evolution of the convective system and its interaction with large-scale environmental conditions. The significant modeling framework does not reproduce every individual MCS track, but rather evaluates whether the model realistically captures long-duration or long-track MCS events and represents the overall statistical behavior of MCS activity in the region. The analysis focuses on the atmospheric processes that support the initiation and maintenance of the system, including moisture transport, thermodynamic instability, and low-level circulation associated with the West African monsoon environment. To assess surface impacts, the study also examines land surface responses during the event, including soil moisture variability and runoff generation in response to intense rainfall. These diagnostics are used to link atmospheric dynamics with hydrological outcomes at the surface. Overall, this work provides a process-based case study of a high-impact MCS event and evaluates the ability of MPAS-A to represent key characteristics of convective systems and their associated hydrological impacts in West Africa.